Simultaneous radioassays of bacterial production and mercury methylation in the periphyton of a tropical and a temperate wetland.

Laboratory radioassays were made to study mercury (Hg) methylation together with bacterial production in the periphyton of two aquatic macrophytes, the submerged Myriophyllum spicatum, from a constructed wetland in Sweden and the floating Eichhornia crassipes, from a eutrophied tropical lake in Brazil. Time course incubations were made by addition of (203)HgCl(2) and the methylmercury formed was extracted at pre-defined time intervals. Bacterial production ((14)C-leucine incorporation) was measured at the same time intervals, with plants removed from parallel incubations made with and without addition of cold HgCl(2). For E. crassipes, higher methylmercury production was observed at elevated bacterial production, whereas for M. spicatum, the bacterial production was significantly lower, and Hg methylation was below the detection limit. The combined results confirm the importance of microbial processes for Hg methylation, although other factors are known to influence this process in complex ways. The addition of Hg did not significantly influence bacterial production, while the incubation temperatures used (25 and 35 degrees C) resulted in different methylation rates. Radiotracer techniques for measurements of bacterial production such as (14)C-leucine uptake can provide useful insights into the Hg cycle in aquatic environments, and our data suggest that they may be used as a proxy of mercury methylation potentials.

129I in Swedish rivers: distribution and sources.

We analyzed the concentration of 129I in the water of 26 rivers covering most of the runoff from Sweden, with the aim of assessing current contamination levels, distribution patterns and potential sources in freshwater systems of northern Europe. The results show relatively high values (up to 1.4 x 10(9) atoms l(-1)), steeply decreasing levels with increasing latitude and a positive correlation with Cl concentration and other chemical parameters. The 129I concentrations observed in south Sweden are probably the highest ever recorded in rivers without any direct discharge from a nuclear installation. The strong latitudinal dependence suggests a northward dilution and possibly depletion of the isotope and a transport from a source located to the south. The most plausible source of the 129I in the studied rivers is atmospheric fallout of 129I emitted either by atmospheric discharges from the nuclear reprocessing facilities at Sellafield (England) and La Hague (France) or by volatilization from seawater contaminated by the same sources. The question is now whether and at what rate the 129I concentration in Nordic watersheds will increase further if discharges from nuclear reprocessing continue.

Relationship of mercury with aluminum, iron and manganese oxy-hydroxides in sediments from the Alto Pantanal, Brazil.

Sediments from nine floodplain lakes in Pantanal were analyzed for a large-scale (300 km) survey of mercury (Hg) load in sediments and soils of the Alto Pantanal and to study the relationship between Hg and reactive aluminum, iron, and manganese oxy-hydroxides. The results were compared with the Hg content in river and stream sediments from the Poconé gold mining area, where Hg has been extensively used and still is in use. The results indicate that the Hg concentrations were elevated in river sediment close to the mining area in Bento Gomes river basin (average in the < 74-microm fraction 88.9 ng Hg g(-1) dry wt.; interquartile range 50.3-119.5), but there was no clear indication that the local Hg emissions have contaminated the remote floodplain lakes, where concentrations were surprisingly low (average in the < 74-microm fraction 33.2 ng Hg g(-1) dry wt. sediment; interquartile range 18.4-46.8), in particular when considering geochemical characteristics of the sediment. The sediment from the floodplain lakes contained less Hg-tot and more reactive iron oxy-hydroxides than soils from the Tapajós area in the Amazon basin. This resulted in a mass ratio between Hg and amorphous oxy-hydroxides of only 5 x 10(-6) for Hg-tot/Fe-oxa (interquartile range 3-7 x 10(-6).

Fish mercury concentration in the Alto Pantanal, Brazil: influence of season and water parameters.

The tropical flood plain Pantanal is one of the world's largest wetlands and a wildlife sanctuary. Mercury (Hg) emissions from some upstream gold mining areas and recent findings of high natural Hg levels in tropical oxisols motivated studies on the Hg cycle in the Pantanal. A survey was made on total Hg in the most consumed piscivorous fish species from rivers and floodplain lakes in the north (Cáceres and Barão de Melgaço) and in the south part of Alto Pantanal (around the confluence of the Cuiabá and Paraguai rivers). Samples were collected in both the rainy and dry seasons (March and August 1998) and included piranha (Serrasalmus spp.), and catfish (Pseudoplatystoma coruscans, pintado, and Pseudoplatystoma fasciatum, cachara or surubim). There was only a small spatial variation in Hg concentration of the 185 analyzed fish samples from the 200 x 200 km large investigation area, and 90% contained total Hg concentration below the safety limit for regular fish consumption (500 ng g(-1)). Concentration above this limit was found in both Pseudoplatystoma and Serrasalmus samples from the Baia Siá Mariana, the only acid soft-water lake included in this study, during both the rainy and dry seasons. Concentration above this limit was also found in fish outside Baia Siá Mariana during the dry season, especially in Rio Cuiabá in the region of Barão de Melgaço. The seasonal effect may be connected with decreasing water volumes and changing habitat during the dry season. The results indicate that fertile women should restrict their consumption of piscivorous fishes from the Rio Cuiabá basin during the dry season. Measures should be implanted to avoid a further deterioration of fish Hg levels.

Mercury net methylation in five tropical flood plain regions of Brazil: high in the root zone of floating macrophyte mats but low in surface sediments and flooded soils.

In aquatic systems, bottom sediments have often been considered as the main methylmercury (MeHg) production site. In tropical floodplain areas, however, floating meadows and flooded forests extend over large areas and can be important Hg methylating sites. We present here a cross-system comparison of the Hg net methylation capacity in surface sediments, flooded soils and roots of floating aquatic macrophytes, assayed by in situ incubation with 203Hg and extraction of formed Me203 Hg by acid leaching and toluene. The presence of mono-MeHg was confirmed by thin layer chromatography and other techniques. Study areas included floodplain lakes in the Amazon basin (Tapajós, Negro and Amazon rivers), the Pantanal floodplain (Paraguay river basin), freshwater coastal lagoons in Rio de Janeiro and oxbow lakes in the Mogi-Guaçú river, São Paulo state. Different Hg levels were added in assays performed in 1994-1998, but great care was taken to standardise all other test parameters, to allow data comparisons. Net MeHg production was one order of magnitude higher (mean 13.8%, range 0.28-35) in the living or decomposing roots of floating or rooted macrophyte mats (Eichhornia azurea, E. crassipes, Paspalum sp., Eleocharis sellowiana, Salvinia sp., S. rotundifolia and Scirpus cubensis) than in the surface layer of underlying lake sediments (mean 0.6%, range 0.022-2.5). Methylation in flooded soils presented a wide range and was in some cases similar to the one found in macrophyte roots but usually much lower. In a Tapajós floodplain lake, natural concentrations of MeHg in soil and sediment cores taken along a lake-forest transect agreed well with data on net methylation potentials in the same samples. E. azurea, E. crassipes and Salvinia presented the highest methylation potentials, up to 113 times higher than in sediments. Methylation in E. azurea from six lakes of the Paraguay and Cuiabá rivers, high Pantanal, was determined in the 1998 dry and wet seasons and ranged from 1.8 to 35%. Methylation was lower in washed roots than in untreated roots of E. azurea and methylation in solids isolated from the roots, was higher than in sediments but lower than in untreated roots. This indicates that the methylation in roots zones occurs mainly in the root-associated solids. Floating meadows are sites of intense production of biomass and of highly bioavailable MeHg and appear to be an essential link of the MeHg cycle in tropical aquatic systems.

The influence of humic substances on the speciation and bioavailability of dissolved mercury and methylmercury, measured as uptake by Chaoborus larvae and loss by volatilization.

The influence of dissolved humic substances (HS) on the bioavailability of dissolved inorganic and methyl mercury (Hg) was quantified by measuring the direct uptake of 203Hg in Chaoborus larvae using laboratory microcosms containing artificial freshwater. The animals were exposed individually in triplicate aquaria at 10 different concentrations of HS covering the whole range found in natural freshwaters (0-110 mg C l(-1)). Mercury-203 concentrations were monitored repeatedly in the same individuals and in their ambient water during up to 10 days. Near-steady state Hg concentrations in Chaoborus were usually reached within 5 days. The bioconcentration factor (BCF, direct uptake only) for the larvae in the absence of HS was 0.55+/-0.09 (S.E.) ml individual(-1) for inorganic Hg and 5.3+/-0.7 ml individual(-1) for methyl Hg, thus showing a 10-fold difference. Normalizing to the organic carbon content of the larvae yields a BCF(OC) in the absence of HS of 2.8+/-0.4 x 10(3) ml (gC)(-1) for inorganic Hg and 2.7+/-0.3 x 10(4) ml (gC)(-1) for methyl Hg. The uptake of both inorganic and methyl Hg decreased markedly with increasing concentration of HS. For inorganic Hg, the decrease in uptake was most pronounced at HS concentrations below 0.2 mg C l(-1). For methyl Hg, the relationship between uptake and log([HS]) was sigmoid, showing a reduction by > 90% when increasing HS concentrations from 1 to 50 mg C l(-1). Similar patterns were observed for losses of Hg from the water phase, mainly through volatilization. These results have implications for both the biouptake and the abiotic cycling of Hg in natural ecosystems and suggest that most dissolved inorganic Hg is bound to dissolved organic matter in most natural freshwaters, whereas dissolved methyl Hg is bound only in humic waters. Assuming that only free aqueous Hg is taken up by the organisms, the rather simple methodology employed here can be used for estimating distribution coefficients (K(OC)) for Hg between HS and water. In this study, the K(OC) values were 2.5+/-0.7 (S.E.) x 10(7) ml (gC)(-1) for inorganic Hg and 1.5+/-0.6 x 10(5) ml (gC)(-1) for methyl Hg. Values of similar magnitude were derived from observed losses of Hg from the water phase, supporting the assumption of an immobilization of both inorganic and methyl Hg by HS. The strong negative influence of dissolved HS on the bioavailability of both inorganic and methyl Hg in freshwater suggests that the high Hg levels often found in fish from humic lakes in the boreal forest zone cannot be explained alone by direct uptake of methyl Hg from the water phase into biota at low trophic levels.

[Treatment of drug dependent patients in general practice]. / Die Behandlung Drogenabhängiger in der Praxis.

After a brief characterization of the actual situation of drug abuse in Switzerland, the general principles of methadone treatment and drug-assisted ambulant withdrawal in the family practice are introduced. They are suited for patients who mainly consume heroin and have a fairly stable social background. Both forms of treatment can very well be offered and carried through by general practitioners, if there is a clear agreement between the patient and the doctor about the therapeutic setting and guidelines. In every case close psychosocial support over a longer time span must be part of the treatment. For this longterm treatment, the continuous relationship with the general practitioner is ideal.

Improved method for the isolation and cultivation of human scalp dermal papilla cells.

We present an improved method for the isolation and cultivation of human scalp anagen hair follicle dermal papilla cells. Following treatment of the isolated dermal papilla with collagenase, incubation in Chang's medium mediates accelerated growth of the papilla cells when compared with other media such as DMEM, M199, and EMEM. Upon reaching confluency, the cells cultured in this fashion exhibit a multilayer-forming property that is dependent on normal proteoglycan synthesis. The papilla cells maintain this morphologic behavior for as long as 7 weeks in culture, or after being subcultured six times. During this time, the cells continue to synthesize extracellular matrix components associated with the human anagen follicle in situ. These include chondroitin sulfate, laminin, and type IV collagen. Type III collagen and keratan sulfate are poorly expressed by the papilla both in situ and in vitro. Heparan sulfate proteoglycan, a matrix component of the papilla in situ, is poorly expressed in vitro. Earlier reports suggested that the expression of extracellular matrix components is not maintained in culture. We show that the expression of these molecules is not dependent on the secondary culture medium, but continues in DMEM and M199 after primary culture in Chang's medium. Our results suggest that initial exposure of the dermal papilla to Chang's medium either selectively permits the outgrowth of papilla cells having extracellular matrix components similar to those found in situ, or stabilizes the expression of extracellular matrix components among the entire cultured cell population.